Exudative age-related macular degeneration (AMD) caused by choroid neovascularization (CNV) is one of the major causes for severe visual impairment in developed countries. Evidence to date suggests that vascular endothelial growth factor (VEGF) plays a central role in the development of CNV. For example, it has been reported that CNV is suppressed by compounds that inhibit the production of VEGF or compounds that inhibit the signal transduction pathway of VEGF. Furthermore, it has also been reported that anti-VEGF antibodies show higher therapeutic efficacy compared to conventional therapeutic methods including photodynamic therapy. Therefore, in recent years, anti-VEGF agents have become a main option for drug therapy against CNV.
VEGF signaling is mediated by two types of receptor tyrosine kinases, i.e., VEGF receptor 1 (VEGFR-1) and VEGF receptor 2 (VEGFR-2). The two receptors are expressed on the human CNV membrane and the laboratory mouse CNV membrane. However, the role of VEGFR-1 signal transduction pathway in CNV is still controversial. For example, one study reports that the inhibition of VEGFR-1 signaling by oral administration of an antibody, gene knockdown, or siRNA inhibits CNV. Another study reports that in the eye, activation of VEGFR-1 by VEGF or placental growth factor 1 (PIGF1), which is a ligand of VEGFR-2, leads to activation of CNV via activation of VEGFR-2 by SPARC. On the other hand, for VEGFR-2, the finding that activation of VEGFR-2 signaling promotes CNV growth is generally accepted. Thus, antiangiogenic approaches targeting VEGFR-2, such as systemic or local administration of anti-VEGFR-2 agents or VEGFR-2 antibodies, and intravitreal administration of siRNA, are expected to inhibit VEGFR-2 signaling and CNV growth.
However, the problem with currently available anti-VEGF agents is that they need to be injected repeatedly at 4- to 6-week intervals. Furthermore, there is a high risk of severe complications such as endophthalmitis and retinal detachment. Therefore, it is desirable to establish a novel therapeutic method that replaces currently used anti-VEGF agents.
A vaccine using a peptide derived from human VEGF receptor 2 is known to induce cytotoxic T-lymphocytes (CTLs) in tumor tissues which have potent cytotoxicity against VEGFR-2-expressing endothelial cells (Patent Document 1). A vaccine using a peptide derived from human VEGF receptor 1 is also known to induce CTLs which have potent cytotoxicity against VEGFR-1-expressing endothelium (Patent Document 2). Furthermore, a vaccine using a peptide derived from VEGF receptor 2 has been confirmed to have CNV inhibitory effects in mice (Patent Document 3). However, as in other tissues, there are many unclear points in the mechanism of neovascularization in the choroid, and the presence of a vaccine that effectively inhibits CNV in human choroid is not known.